1. Field of the Invention
The present invention relates to a DC motor control apparatus and a recording apparatus.
2. Related Background Art
Recently, both improvement of image quality and a decrease in moving sound are demanded in a printer. Particularly in an inkjet recording apparatus in which the number of noise sources are small during recording, noise reduction is realized by using a DC motor and a linear encoder as driving means for scanning a recording head.
Further, the DC motor and a rotary encoder are being adopted as driving means for conveying paper. With reference to the noise reduction, such an effect can be expected only by adopting the DC motor. However, in order to convey the paper with high accuracy, high degrees of a stopping control technology and mechanical accuracy are essential.
A technique in which torque of the DC motor is dropped down to zero to stop the DC motor by inertia when the rotation of a roller reaches a target stop position is basically adopted as the method of stopping the DC motor (stopping control).
In addition to the above-described technique, there is proposed a method in which the DC motor is stopped by interrupting passage of electric current to the DC motor after a predetermined time elapses from a time when the rotation of the DC motor is expected to reach a predetermined position in front of the target stop position on the basis of velocity information at a position in front of the target stop position by a predetermined distance.
However, when the torque of the DC motor is dropped down to zero at the target stop position, disturbance (force) is generated in stopping the DC motor by deformation of torque transferring means for transferring the torque of the DC motor (torque transferring member) such as a belt and a gear. Hereinafter the force (disturbance) is referred to as “elastic deformation charging force” in the description. The elastic deformation charging force is generated as the torque in an opposite direction to a drive direction of a driven body. When the torque of the DC motor is dropped down to zero at the target stop position, the driven body is moved by the elastic deformation charging force and the position shift occurs at the stop position.
FIG. 11 is an explanatory view showing the occurrence of the position shift. The sign En represents a position signal based on an encoder signal. For example, in an arrow MV1, a stopping process is performed at timing of En and the front end of a recording medium conveyed by conveying means is stopped at a position Pn (for the sake of convenience, the moving distance is set to zero until the front end of the recording medium is stopped after the stopping process is performed). However, the front end of the recording medium is moved by a distance d and stopped at a position Pn−1 due to the elastic deformation charging force (arrow MV2).
Therefore, when the passage of the electric current to the DC motor is interrupted at the target stop position or in front of the target stop position during servo drive at low velocity, the stop position is shifted by the elastic deformation charging force, and stopping accuracy is worsened.